U.S. Pat. No. 4,569,471 to Ingemansson et al. describes a process and apparatus for feeding lengths of a continuous glass fiber strand into a muffler outer shell. The apparatus includes a nozzle for expanding the fiber strand into a wool-like material before the material enters the outer shell. In a first embodiment, filling of an outer cylinder of the muffler shell occurs without an end-piece joined to the outer cylinder. After the filling operation is completed, the outer cylinder is moved to a separate station where the end piece is welded onto the outer cylinder. During movement of outer cylinder, a vacuum device may remain coupled to the outer cylinder or a cover is placed over the filled outer cylinder so as to prevent the wool-like material from coming out during transport, see column 4, lines 1–7. During the closure process, great care must be taken to ensure that glass fiber material does not extend into the joint area.
In a second embodiment, a perforated pipe/outer end piece assembly is positioned only part way into the muffler outer cylinder during the glass material filling operation. After the filling operation has been completed, the perforated pipe/end piece assembly is moved to its final position within the outer cylinder.
While the technology of Ingemansson et al. improved many aspects of muffler technology, it does have certain drawbacks. For example, the filling of the interior of the muffler, or sections of the interior of the muffler, is typically limited to certain geometries. Thus, for example, mufflers having odd shapes, such as clamshell mufflers, are difficult to fill using the current technology.
Further, the filling of the interior region must be done after the build-out of an entire muffler cavity, including the introduction and fixing of the internal mechanical parts (tubes and partitions) within the outer shell of the muffler. As stated above, this thus limits the filling of the sections of the interior of the muffler due to space constraints and other considerations.